Bacteria-based and enzyme-based mechanisms and products for viscosity reduction breaking of viscoelastic fluids

ABSTRACT

It has been discovered that fluids viscosified with viscoelastic surfactants (VESs) may have their viscosities reduced (gels broken) by the direct or indirect action of a biochemical agent, such as bacteria, fungi, and/or enzymes. The biochemical agent may directly attack the VES itself, or some other component in the fluid that produces a by-product that then causes viscosity reduction. The biochemical agent may disaggregate or otherwise attack the micellar structure of the VES-gelled fluid. The biochemical agent may produce an enzyme that reduces viscosity by one of these mechanisms. A single biochemical agent may operate simultaneously by two different mechanisms, such as by degrading the VES directly, as well as another component, such as a glycol, the latter mechanism in turn producing a by-product (e.g. an alcohol) that causes viscosity reduction. Alternatively, two or more different biochemical agents may be used simultaneously. In a specific, non-limiting instance, a brine fluid gelled with an amine oxide surfactant can have its viscosity broken with bacteria such as  Enterobacter colacae, Pseudomonas fluorescens, Pseudomonas aeruginosa , and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Pat. No. 7,052,091issued May 30, 2006, which in turn claims the benefit of U.S.provisional application No. 60/244,804 filed Oct. 31, 2000.

FIELD OF THE INVENTION

The present invention relates to gelled treatment fluids used duringhydrocarbon recovery operations, and more particularly relates, in oneembodiment, to methods of “breaking” or reducing the viscosity ofaqueous treatment fluids containing viscoelastic surfactant gellingagents used during hydrocarbon recovery operations.

BACKGROUND OF THE INVENTION

Hydraulic fracturing is a method of using pump rate and hydraulicpressure to fracture or crack a subterranean formation. Once the crackor cracks are made, high permeability proppant, relative to theformation permeability, is pumped into the fracture to prop open thecrack. When the applied pump rates and pressures are reduced or removedfrom the formation, the crack or fracture cannot close or healcompletely because the high permeability proppant keeps the crack open.The propped crack or fracture provides a high permeability pathconnecting the producing wellbore to a larger formation area to enhancethe production of hydrocarbons.

The development of suitable fracturing fluids is a complex art becausethe fluids must simultaneously meet a number of conditions. For example,they must be stable at high temperatures and/or high pump rates andshear rates that can cause the fluids to degrade and prematurely settleout the proppant before the fracturing operation is complete. Variousfluids have been developed, but most commercially used fracturing fluidsare aqueous based liquids that have either been gelled or foamed. Whenthe fluids are gelled, typically a polymeric gelling agent, such as asolvatable polysaccharide, is used. The thickened or gelled fluid helpskeep the proppants within the fluid. Gelling can be accomplished orimproved by the use of crosslinking agents or cross-linkers that promotecrosslinking of the polymers together, thereby increasing the viscosityof the fluid.

The recovery of fracturing fluids may be accomplished by reducing theviscosity of the fluid to a low value so that it may flow naturally fromthe formation under the influence of formation fluids. Crosslinked gelsgenerally require viscosity breakers to be injected to reduce theviscosity or “break” the gel. Enzymes, oxidizers, and acids are knownpolymer viscosity breakers. Enzymes are effective within a pH range,typically a 2.0 to 10.0 range, with increasing activity as the pH islowered towards neutral from a pH of 10.0. Most conventional boratecrosslinked fracturing fluids and breakers are designed from a fixedhigh crosslinked fluid pH value at ambient temperature and/or reservoirtemperature. Optimizing the pH for a borate crosslinked gel is importantto achieve proper crosslink stability and controlled enzyme breakeractivity.

While polymers have been used in the past as gelling agents infracturing fluids to carry or suspend solid particles as noted, suchpolymers require separate breaker compositions to be injected to reducethe viscosity. Further, such polymers tend to leave a coating on theproppant and a filter cake of dehydrated polymer on the fracture faceeven after the gelled fluid is broken. The coating and/or the filtercake may interfere with the functioning of the proppant. Studies havealso shown that “fish-eyes” and/or “microgels” present in some polymergelled carrier fluids will plug pore throats, leading to impairedleakoff and causing formation damage.

Recently it has been discovered that aqueous drilling and treatingfluids may be gelled or have their viscosity increased by the use ofnon-polymeric viscoelastic surfactants (VES). These VES materials areadvantageous over the use of polymer gelling agents in that they do notdamage the formation, leave a filter cake on the formation face, coatthe proppant or create microgels or “fish-eyes”. It is still necessary,however, to provide some mechanism that will break the viscosity ofVES-gelled fluids.

It is known to use bacteria in biodegradation, bioremediation, ormicrobe enhanced oil recovery (MEOR) techniques. Bacteria are primarilyknown to decompose reservoir hydrocarbons to produce more easilyproducible fluids, or to decompose hydrocarbon-based pollutants toenvironmentally acceptable states.

It is also known that bacteria will degrade drilling fluids. U.S. Pat.No. 3,612,178 discloses a flow-stimulating liquid solution and methodsof used based primarily on the combination of a linear alkyl sulfonateas a detergent and penetrant, serving as a special carrier for a lauricamide emulsifier to draw oil into an emulsion and for a phosphate, assodium phosphate, to draw water into the emulsion. A preservative isadded to inhibit deterioration due to bacteria. Similarly, U.S. Pat. No.3,800,872 relates to methods for recovery of petroleum from asubterranean formation which include injecting into the formation anaqueous flooding medium which assumes a viscosity in oil-rich portionsof the formation that is significantly less than the viscosity assumedin the portions low in oil content, the flooding medium therebypreferentially driving the oil, as opposed to water, from the formation.The flooding medium may include a material such as guar that imparts ahigh viscosity but is subject to rapid degradation by the bacteria inthe formation, and a poisoning agent for the bacteria, such asorthocresol, which is preferentially soluble in oil. The use of bacteriato directly digest or degrade polymeric gels used in fracturing is alsoknown. However, it is presently unknown to use bacteria and/or enzymesto break viscosities of fluids gelled using viscoelastic surfactants.

General background information concerning biodegrading surfactants maybe found in D. R. Karsa, et al., ed., Biodegradability of Surfactants,Blackie Academic & Professional, 1995.

It would be desirable if a viscosity breaking system could be devised tobreak the viscosity of fracturing fluids gelled with viscoelasticsurfactants.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for breaking the viscosity of aqueous treatment fluids gelledwith viscoelastic surfactants (VESs).

It is another object of the present invention to provide compositionsand methods for breaking VES-surfactant substrates fluids usingbacteria.

Still another object of the invention is to provide additional methodsand VES fluid compositions for breaking the viscosity of aqueous fluidsgelled with viscoelastic surfactants.

Yet another object of the invention is to provide methods andcompositions for breaking the viscosity of aqueous fluids gelled withviscoelastic surfactants using bio-produced compounds such as lipaseenzymes.

Still another object of the invention is to provide methods andcompositions for breaking the viscosity of aqueous fluids gelled withvisoelastic surfactants using bio-produced compounds such assurfactants, solvents, or acid.

In carrying out these and other objects of the invention, there isprovided, in one form, a method for breaking viscosity of aqueous fluidsgelled with a viscoelastic surfactant (VES) that involves adding to anaqueous fluid gelled with at least one viscoelastic surfactant, aviscosity-breaking biochemical agent in an amount effective to reducethe viscosity of the gelled aqueous fluid. Suitable biochemical agentsinclude bacteria, fungi, enzymes, and combinations thereof.

In another embodiment, the invention involves a method for breakingviscosity of aqueous fluids gelled with viscoelastic surfactants byadding to an aqueous fluid gelled with at least one viscoelasticsurfactant, at least one bacteria type in an amount effective to reducethe viscosity of the VES-gelled aqueous fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of viscosity reduction over time employing 10% byvolume (bv) Enterobacter colacae in a 3% KCl fluid gelled with 2% TAPAOat 125° F. (52° C.) and ambient pressure;

FIG. 2 is a graph of viscosity reduction over time employing 10% byvolume Pseudomonas fluorescens in a 3% KCl fluid gelled with 2% TAPAO at75° F. (24° C.) and ambient pressure;

FIG. 3 is a graph of viscosity reduction over time employing 10% byvolume Pseudomonas aeruginosa in a 3% KCl fluid gelled with 2% TAPAO at75° F. (24° C.) and ambient pressure;

FIG. 4 is a graph of viscosity reduction over time employing 1.0% and3.0% by volume (bv) Pseudomonas aeruginosa esmeralda X-3C (EPA X-3C) ina 3% KCl fluid gelled with 6.0% bv TAPAO at 180° F. (82° C.) and 950 psi(6.5 kPa);

FIGS. 5, 6, 7, and 8 chart the effects of various bacteria nutrients onthe viscosity reduction of 6.0% TAPAO at 180° F. (82° C.) and 400 psi(2.8 kPa); and

FIG. 9 is a graph of viscosity reduction over time employing 1.0% bvPseudomonas aeruginosa esmeralda X-3C (EPA X-3C) with and without 0.2%bv Limonene in a 3% KCl fluid gelled with 6.0% bv TAPAO at 180° F. (82°C.) and 950 psi (6.5 kPa).

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that various biochemical agents, such as bacteriaand enzymes, will directly degrade or digest the gel created by variousviscoelastic surfactants (VESs) in an aqueous fluid, or the biochemicalagents will degrade or digest other materials in the viscosified fluidsuch as alcohols, glycols, starches, potassium or other formate, and thelike to produce by-products that will reduce the viscosity of the gelledaqueous fluid either directly, or by disaggregation or rearrangement ofthe VES micellar structure.

That is, in various non-limiting embodiments of the invention:

-   -   1. the biochemical agent (bacteria, fungus, and/or enzyme) will        attack and break down the surfactant itself, using the        surfactant molecule as its carbon source;    -   2. the biochemical agent (bacteria, fungus, and/or enzyme) will        attack and break down another component in the VES-gelled        aqueous fluid, whether already present or intentionally added as        a carbon source for the bio-chemical agent, including, but not        limited to, alcohols, monoalcohol polymers, alcohol fatty acids,        alkyl fatty acids, glycols, starches, potassium or other        formate, polysaccharides, sugars, sugar chelants, sugar        alcohols, aliphatic alcohols, reservoir crude oils, proteins,        VES stabilizers, amino acids, acetates, phosphonates,        phospholipids, lactates, isocyanates, esters, turpenes,        butyrates, propionates, salicylates, hexaonates,        nitrilotriacetic acid, ethylenediaminetetraacetic acid, amino        chelant compounds (e.g. hydroxyethyliminodiacetic acid),        polyaspartates, pyrrolidone compounds, and mixtures thereof;    -   3. the biochemical agent (bacteria, fungus, and/or enzyme) will        reduce the viscosity of the VES-gelled fluid by disrupting the        VES micellar structure by disaggregating the VES micelles        (causing them not to be aggregated together) or rearranging the        VES micellar structure (from rod- or worm-shape to spherical);    -   4. the biochemical agent may be a bacteria and/or fungus which        in turn secrets an enzyme that reduces the viscosity of the        VES-gelled aqueous fluid by:    -   a. directly attacking and digesting or otherwise breaking down        the viscoelastic surfactant itself or catalyzing a reaction to        do so;    -   b. attacking and digesting or otherwise breaking down a        component of the fluid other than the viscoelastic surfactant        that in turn produces a by-product that reduces the viscosity of        the VES-gelled aqueous fluid or catalyzing a reaction to do so;        and    -   c. disaggregating the VES micelles or rearranging the VES        micellar structure, or producing a by-product that does so,        through catalysis or other mechanism.

The use of enzymes could be very complex. For instance, the enzyme couldremove a part of the surfactant molecule, such as the “head” and/or“tail” portions to alter its structure. Or the enzyme could “add”another material or functionality, such as ammonium or phosphate, to the“head” group that would alter its surfactant properties and disrupt themicellar structure.

It will be also appreciated that the biochemical agent, such as bacteriaor fungus, may be biotechnically engineered to serve the functionsdescribed. There are several biotechnologies that can be employed.Growth challenge, selective gene expression, radiated for selective geneexpression, and gene splicing (genetically modified organisms) are justa few non-limiting examples of applicable biotechnical techniques torefine the practice of this art.

In particular, various combinations of these approaches may be used tobe sure that the viscosity of the fluid is completely reduced through avariety of mechanisms. Indeed, a particular blend of biochemical agentsmay be custom designed for a particular VES fluid system.

It is expected that the biochemical agent can be used to reduce theviscosity of a VES-gelled aqueous fluid regardless of how the VES isultimately utilized. For instance, the biochemical agent viscositybreaking mechanism could be used in all VES applications including, butnot limited to, VES-gelled friction reducers, VES viscosifiers for losscirculation pills, fracturing fluids, gravel pack fluids, viscosifiersused as diverters in acidizing, VES viscosifiers used to clean updrilling mud filter cake, remedial clean-up of fluids after a VEStreatment (post-VES treatment), and the like. One key feature to the useof bacteria as a VES degradation mechanism is that many bacteria havetheir own mobility, as contrasted with other VES clean-up fluids thatmust be transported by another means to the gel. That is, many bacteriahave enhanced mobility due to the flagella propulsion characteristicthat will permit them to move and contact needed VES placement sites.This is an advantage over mere chemical diffusion movement mechanismsthat solvents or other agents might have.

A value of the invention is that a fracturing or other fluid can bedesigned to have enhanced breaking characteristics. Importantly, betterclean-up of the VES fluid from the fracture and wellbore can be achievedthereby. Better clean-up of the VES directly influences the success ofthe fracture treatment, which is an enhancement of the well'shydrocarbon productivity.

In order to practice the method of the invention, an aqueous fracturingfluid, as a non-limiting example, is first prepared by blending a VESinto an aqueous fluid. The aqueous fluid could be, for example, water,brine, aqueous-based foams or water-alcohol mixtures. Any suitablemixing apparatus may be used for this procedure. In the case of batchmixing, the VES and the aqueous fluid are blended for a period of timesufficient to form a gelled or viscosified solution. The VES that isuseful in the present invention can be any of the VES systems that arefamiliar to those in the well service industry, and may include, but arenot limited to, amines, amine salts, quaternary ammonium salts,amidoamine oxides, amine oxides, mixtures thereof and the like. Suitableamines, amine salts, quaternary ammonium salts, amidoamine oxides, andother surfactants are described in U.S. Pat. Nos. 5,964,295; 5,979,555;and 6,239,183, incorporated herein by reference. Materials sold underU.S. Pat. No. 5,964,295 include ClearFRAC™, which may also comprisegreater than 10% of a glycol. One preferred VES is an amine oxide. Aparticularly preferred amine oxide is tallow amido propylamine oxide(TAPAO), sold by Baker Oil Tools as SurFRAQ™ VES. SurFRAQ is a VESliquid product that is 50% TAPAO and 50% propylene glycol. Theseviscoelastic surfactants are capable of gelling aqueous solutions toform a gelled base fluid.

The amount of VES included in the fracturing fluid depends on twofactors. One involves generating enough viscosity to control the rate offluid leak off into the pores of the fracture, and the second involvescreating a viscosity high enough to keep the proppant particlessuspended therein during the fluid injecting step, in the non-limitingcase of a fracturing fluid. Thus, depending on the application, the VESis added to the aqueous fluid in concentrations ranging from about 0.5to 12.0% by volume of the total aqueous fluid (5 to 120 gallons perthousand gallons (gptg)). The most preferred range for the presentinvention is about 1.0 to about 6.0% by volume VES product.

Propping agents are typically added to the base fluid after the additionof the VES. Propping agents include, but are not limited to, forinstance, quartz sand grains, glass and ceramic beads, bauxite grains,walnut shell fragments, aluminum pellets, nylon pellets, and the like.The propping agents are normally used in concentrations between about 1to 14 pounds per gallon (120-1700 kg/m³) of fracturing fluidcomposition, but higher or lower concentrations can be used as thefracture design required. The base fluid can also contain otherconventional additives common to the well service industry such as waterwetting surfactants, non-emulsifiers and the like. As noted, in thisinvention, the base fluid can also contain other non-conventionaladditives which can contribute to the bacteria-breaking action of theVES fluid, and which are added for that purpose.

In one non-limiting embodiment of the invention, suitable bacteria foruse in the invention that directly digest viscoelastic surfactantsinclude, but are not necessarily limited to, those in the classesEnterobacter, Enterococcus, Pseudomonas, Bacillus, Leptospirillum,Clostridium, Arthrobacter, Rhodobacter, Rhodococcus, Micrococcus,Serratia, Thermoanaerobacter, Thiobacillus, Pyrococcus, Lactobacillus,Achromobacter, Propionibacterium, Thermomicrobium, Nitrobacter,Nitrosomonas, Sulfolobus, Methanobacterium, Methanococcus, Bacteroides,Fusobacterium, Syntrophus, Acetogenium, Actinomyces, Acetobacter,Citrobacter, Alteromonas, Acinetobacter, Flavobacterium,Corynebacterium, and the like and mixtures thereof.

In one non-limiting embodiment of the invention, suitable bacteria foruse in the embodiment of the invention that directly digest viscoelasticsurfactants include, but are not necessarily limited to, Arthrobacterglobiformis, Enterobacter colacae, Lactobacillus sporogenes,Lactobacillus bulgaricus, Lactobacillus acidophillus, Pseudomonasfluorescens, Pseudomonas aeruginosa, Actinomyces israeli, Pseudomonasputida, Nitrobacter vulgaris, Arthrobactor M153B, Bacillus megaterium,Thiobacillus novellus, Bacillus subtilis, Bacillus licheniformis,Clostridium pasteurianum, Corynebacterium glucuronolyticum, Enterococcusfaecalis, Pyrococcus abyssi, Rhodococcus ST-5, Rhodococcus 33,Rhodococcus H13-A, Thermoanaerobacter ethanolicus, Thermoanaerobactermathranii, Nitrosomonas europaea, Propionibacterium propionicus,Rhodobacter sphaeriodes, Clostridium thermocellum, Clostridium ATCC#53797, Clostridium ATCC #53793, Corynebacterium hydrocarbolastus,Acetomicrobium flavidum, Acetobacter pasteurianus, Serratia marcescens,Acetobacter aceti, Achromobacter xylosoxidans, and mixtures thereof.

In another non-limiting embodiment where glycol is present or added tothe VES-gelled fluid, suitable glycol-splitting bacteria may include,but are not necessarily limited to, Pseudomonas fluorescens, Pseudomonasstutzeri, Pseudomonas aeruginosa, Pseudomonas putida, Acinetobacteranitratus, Bacillus subtilis, Bacillus licheniformis, Clostridiumpasteurianum, Rhodococcus ST-5, and mixtures thereof.

In another non-limiting embodiment of the invention, fluid temperature,pressure, and pH can aid microbe metabolic activity. Increase intemperature up to as much as 250° F. (121° C.) and fluid pH betweenabout 4.0 and about 9.0 enhances microbe metabolic activity. Increase influid pressure up to as much as 22,000 psi (152 kPa) can also enhancemicrobe metabolic activity.

In another non-limited embodiment inorganic and organic nutrients areadded to aid microbe metabolic activity. Inorganic nutrients mayinclude, but are not necessarily limited to, nitrites, nitrates,sulfites, sulfates, chlorides, phosphates, and mixtures thereof. Organicnutrients may include, but are not necessarily limited to, urea, aminoacids, proteins, lipids, tryptic soy broth (TSB), agar, glucose, sugars,polysaccharides, turpenes, phosphonates, glycols, and mixtures thereof.

In the embodiments where enzymes, such as lipases, are produced bybacteria and other microorganisms, the by-products, also termedbio-products, can be selectively extracted or pulled out of themicroorganism solution, as is common with enzyme products. Thesebio-products can then be pumped or otherwise directed into the VESsurfactant to reduce its viscosity. The producing biochemical agent,such as bacteria or fungus would not itself be delivered to theVES-gelled fluid.

Besides lipase, other suitable enzymes include, but are not necessarilylimited to oxidase, hydrolase, transferase, and mixtures thereof.

The biochemical agent may be a fungi including, but not necessarilylimited to, Candida antarctica, Candida tropicalis, Candida rugosa,Candida albicans, Candida cylindralea, Trichoderma reesei, Aspergillusniger, Aspergillus oryzae, Saccharomyces cerevisiae, Saccharomycesdiastaticus, and mixtures thereof.

Any or all of the above biologically produced by-products may beprovided in an extended release form such as encapsulation by polymer orotherwise, pelletization with binder compounds, absorbed on a poroussubstrate, and/or a combination thereof. Specifically, the enzymes andother bio-products may be encapsulated to permit slow or timed releasethereof. In non-limiting examples, the coating material may slowlydissolve or be removed by any conventional mechanism, or the coatingcould have very small holes or perforations therein for the bio-productswithin to diffuse through slowly. For instance, polymer encapsulationcoatings such as used in fertilizer technology available from ScottsCompany, specifically POLY-S® product coating technology, or polymerencapsulation coating technology from Fritz Industries could possibly beadapted to the methods of this invention. The bio-produced enzymes couldalso be absorbed onto zeolites, such as Zeolite A, Zeolite 13X, ZeoliteDB-2 (available from PQ Corporation, Valley Forge, Pa.) or ZeolitesNa-SKS5, Na-SKS6, Na-SKS7, Na-SKS9, Na-SKS10, and Na-SKS13, (availablefrom Hoechst Aktiengesellschaft, now an affiliate of Aventis S.A.), andother porous solid substrates such as MICROSPONGE™ (available fromAdvanced Polymer Systems, Redwood, Calif.) and cationic exchangematerials such as bentonite clay. Further, the bio-products may be bothabsorbed into and onto porous substrates and then encapsulated orcoated, as described above.

It is difficult, if not impossible, to specify with accuracy the amountof the biochemical agent and/or biologically produced by-product thatshould be added to a particular aqueous fluid gelled with viscoelasticsurfactants to sufficiently or fully break the gel, in general. Forinstance, a number of factors affect this proportion, including but notnecessarily limited to, the particular VES used to gel the fluid; theparticular biochemical agent used; the temperature of the fluid; thedownhole pressure of the fluid, the starting pH of the fluid; and thecomplex interaction of these various factors. Nevertheless, in order togive an approximate feel for the proportions of the bacteria to be usedin the method of the invention, the amount of biochemical agent addedmay range from about 0.01 to about 20.0 volume %, based on the totalweight of the fluid; preferably from about 0.1 to about 2.0 volume %.

In a typical fracturing operation, the fracturing fluid of the inventionis pumped at a rate sufficient to initiate and propagate a fracture inthe formation and to place propping agents into the fracture. A typicalfracturing treatment would be conducted by mixing a 20.0 to 60.0gallon/1000 gal water (volume/volume—the same values may be used withany SI volume unit, e.g. 60.0 liters/-1000 liters) amine oxide VES, suchas SurFRAQ, in a 2% (w/v) (166 lb/1000 gal, 19.9 kg/m³) KCl solution ata pH ranging from about 6.0 to about 8.0. The bio-chemical agent oragents are added after the VES addition.

The various embodiments of the invention are summarized below.

-   -   1. The viscosity of the VES-gelled fluid may be reduced by the        use of a biochemical agent (bacteria, fungus, enzyme, etc.) that        will directly attack and break down the VES surfactant, such as        by digestion, using the viscoelastic surfactant molecule as its        carbon source. Suitable bacteria that can lower viscosity by        this mechanism include, but are not necessarily limited to        Pseudomonas fluorescens, Pseudomonas stutzeri, Enterobacter        cloacae, Corynebacterium glucoronlyticum, Enterococcus faecalis,        Pseudomonas aerugnosa, Pseudomonas putida, Acinetobacter        anitratus, Serratia marcescens, Nitrobacter vulgaris,        Clostridium thermocellum, Thermoanaerobacter ethanolicus,        Clostridium pasteurianum, Rhodococcus ST-5, and mixtures        thereof.    -   2. The viscosity of the VES-gelled fluid may be reduced by a        biochemical agent (bacteria, fungus, enzyme, etc.) that will        directly attack and break down another component in the fluid        besides the VES surfactant. This other component could be one        that is normally added to the VES fluid in the normal course of        operations, such as a glycol solvent for the VES surfactant        itself, or it could be added solely for the purpose of providing        a food source, i.e. carbon source or energy source for the        biochemical agent, such as sugars and proteins. Such compounds        include, but are not necessarily limited to, alcohols, monoalkyl        alcohol polymers, alcohol fatty acids, alkyl fatty acids,        glycols, starches, potassium formate or other formate,        polysaccharides, sugars, sugar chelants, sugar alcohols,        aliphatic alcohols, reservoir crude oils, proteins, VES        stabilizers, amino acids, acetates, isocyanates, esters,        lactates, butyrates, turpenes, propionates, salicylates,        phosphonates, phospholipids, hexaonates, nitrilotriacetic acid,        ethylenediaminetetraacetic acid, polyaspartates, amine chelant        compounds (e.g. hydroxyethyliminodiacetic acid), pyrrolidone        compounds, and mixtures thereof. In one non-limiting example,        the biochemical agent could operate on the propylene glycol in        SurFRAQ to produce one or more bio-alcohols or bio-surfactants        that will directly degrade the VES gel. The alcohol or        bio-surfactant causes the micelles to change from rod-shaped to        sphere-shaped, or disperses or disaggregates the micellar        structure of the VES-gelled surfactant.    -   3. The viscosity of the VES-gelled fluid may be reduced by a        biochemical agent (bacteria, fungus, enzyme, etc.) that will        disaggregate, disorganize, rearrange or otherwise disrupt the        VES micellar structure to the extent that the viscosity is        reduced.    -   4. The viscosity of the VES-gelled fluid may have its viscosity        reduced by use of a biochemical agent, in this case a bacteria        or fungus, which secrets an enzyme that in turn reduces the        viscosity of the VES-gelled fluid by one of the discussed        mechanisms, namely (a) directly attacking and digesting or        otherwise breaking down the VES itself, or producing a        by-product that does so, (b) attacking or breaking down a        component of the fluid other than the VES, such as an alcohol,        glycol, turpene or the like which is already present in the        fluid, or is added for the specific purpose of reaction with the        generated enzyme, or the enzyme produces a by-product that does        so, and/or (c) disaggregating the VES micelles, or producing a        by-product that does so.    -   5. The rate of microbe metabolic activity of the bacteria,        fungi, and/or enzymes can be enhanced by an increase in fluid        temperature, such as up to 180° F. (82° C.); by controlling        fluid pH, such as to about 7.5 pH; and by increasing fluid        pressure, such as pressures greater than about 600 psi (4.1        kPa). In one non-limiting embodiment of the invention, the pH        adjustment is to a range between about 2.0 and about 11.0,        preferably between about 3.0 and about 9.0 pH.

It will be appreciated that one biochemical agent, such as a particularbacteria type, may function to reduce viscosity by more than onemechanism in a particular VES system. For instance, a particularbacteria type may directly digest the VES itself, while also digestingpropylene glycol that may be present to produce lipase that also acts onthe VES, such as by catalysis, to also break down the surfactantmolecules. Alternatively more than one bacteria type could be used,where the different bacteria operate by the same or different mechanismsas outlined above. Further, a bacteria and an enzyme could be usedtogether. Other mechanism combinations are expected to be useful aswell.

In one embodiment of the invention, the method of the invention ispracticed in the absence of gel-forming polymers and/or gels or aqueousfluid having their viscosities enhanced by polymers.

Suitable bio-surfactants include, but are not necessarily limited to thegroup of glycolipid, phospholipids, lipopeptide, peptidolipids, neutrallipids, polysaccharide-fatty acid complexes, polysaccharide-proteincomplexes, and mixtures thereof. Suitable bio-solvents include, but arenot necessarily limited to the group of methanol, ethanol, butanol,acetone, and mixtures thereof. Suitable bio-acids include, but are notnecessarily limited to the group of formic, acetic, lactic, pyruvic,nitric acids, and mixtures thereof.

The present invention will be explained in further detail in thefollowing non-limiting Examples that are only designed to additionallyillustrate the invention but not narrow the scope thereof. Theseparticular Examples further illustrate the embodiment of the inventionwhere bacteria are the biochemical agent used to reduce the viscosity ofa VES-gelled fluid by directly digesting the VES surfactant.

GENERAL PROCEDURE FOR EXAMPLES 1-3

To a Waring blender were added 500 mls of distilled water, 10 grams ofKCl, followed by 5.0 to 10.0 mis of viscoelastic surfactant (such asSurFRAQ TAPAO available from Baker Hughes, used in the Examples). Theblender was used to mix the components on a very slow speed, to preventfoaming, for about 15 minutes to viscosify the VES fluid. Mixed sampleswere then placed into 500 ml wide mouth Nalgene plastic bottles.VES-breaking bacteria were then added to each sample, and the sample wasshaken vigorously for 60 seconds. The samples were placed in a waterbath at the indicated temperature and visually observed every 30 minutesfor viscosity reduction difference between the samples. The sample withfast-acting bacteria such as Enterobacter colacae from Micro-TES Inc.lost viscosity noticeably quickly (Example 1; FIG. 1). Most gel breakingoccurred over the first 24 hour period with additional breakingcontinuing during a 48 to 96 hour period.

Viscosity reduction can be visually detected. Shaking the samples andcomparing the elasticity of gel and rate of air bubbles rising out ofthe fluid can be used to estimate the amount of viscosity reductionobserved. Measurements using a Fann 35 rheometer at 100 rpm can also beused to acquire quantitative viscosity reduction of each sample. Thepreferred method of measurement is by using of a Fann 50 rheometer,where increases in temperature and pressure can be applied, simulatingdown hole temperature. The pressure limitation of a Fann 50 rheometer is1000 psi (6.9 kPa).

Examples 1-3

FIGS. 1-3 show the results of Examples 1-3, respectively, charting theeffects of using the indicated bacteria at 10% by volume concentrations.It may be seen that the SurFRAQ viscosity broke most quickly withEnterobacter colacae, losing most of its viscosity in the first 2-3hours (Ex. 1, FIG. 1). Viscosity reduction was also more complete inthis Example 1. Pseudomonas fluorescens (Ex. 2, FIG. 2) and Pseudomonasaeruginosa (Ex. 3, FIG. 3) gave viscosity reduction as well, but moregradually than Enterobacter colacae. All Examples were run using 2%TAPAO in 3% KCl. Example 1 (FIG. 1) was conducted at 125° F. (52° C.);Examples 2 and 3 (FIGS. 2 and 3, respectively) were conducted at 75° F.(24° C.).

Examples 4 AND 9

FIGS. 4 and 9 show the results of Examples 4 and 9, respectively. BothExamples use 6.0% bv TAPAO surfactant at 180° F. (82° C.) and 950 psi(6.5 kPa) on a Fann 50 rheometer. Both compositions contained 3% KCl.The order of mixing was: DI water, KCl, NH₄NO₃, TSB, Limonene (if used),EPA X-3C, TAPAO. The nutrient package for both Examples was 30.0 pptg(3.4 kg/m³) NH₄PO₃, 30 pptg (3.4 kg/m³) NH₄NO₃, and 15.0 pptg (1.7kg/M³), Tryptic Soy Broth (TSB).

FIG. 4 shows a highly modified strain of Pseudomonas aeruginosaesmeralda X-3C from Micro-TES, Inc., can completely degrade the TAPAOviscosity within 10 to 12 days at 1.0% to 3.0% bv addition. FIG. 9 showsthe EPA X-3C strain at 1.0% concentration in the 6% bv TAPAO with andwithout 0.2% Limonene. The data show enhanced microbe metabolic activityin the Limonene addition test.

Examples 5-8

FIGS. 5-8 show the results of Examples 5-8, respectively, charting theeffects of various bacteria or microbe nutrients on 6% bv TAPAOsurfactant at 180° F. (82° C.) and 950 psi (6.5 kPa). It may be seenthat proper selection of microbe nutrient is possible that has minimaleffects on the TAPAO viscosity.

All of Examples 5-8 used a Fann 50 rheometer at 180° F. (82° C.) at 400psi (2.8 kPa). Examples 5-7 used 6% TAPAO, 3% KCl, 30 pptg (3.4 kg/m³)NH₄PO₃ and NH₄NO₃ combined, and 20.0 pptg (2.4 kg/m³) TSB. Example 8used 6% TAPAO and 3% KCl with the indicated additives. EGMBE in Example6 refers to ethylene glycol monobutyl ether.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in providing methods and compositions for a VES fracturingfluid breaker mechanism. However, it will be evident that variousmodifications and changes can be made thereto without departing from thebroader spirit or scope of the invention as set forth in the appendedclaims. Accordingly, the specification is to be regarded in anillustrative rather than a restrictive sense. For example, specificcombinations of viscoelastic surfactants, biochemical agents, and othercomponents falling within the claimed parameters, but not specificallyidentified or tried in a particular composition or fluid, areanticipated to be within the scope of this invention.

1-32. (canceled)
 33. An aqueous fluid comprising: water; at least oneviscoelastic surfactant (VES) in an amount effective to increase theviscosity of the aqueous fluid; at least one biochemical agent in anamount effective to reduce the viscosity of the gelled aqueous fluid,where the biochemical agent is selected from the group consisting ofbacteria, fungi, enzymes, and combinations thereof, where thebiochemical agent reduces the viscosity of the gelled aqueous fluid bydisaggregating or rearranging a micelle structure of the VES. 34.(canceled)
 35. The fluid of claim 33 where the biochemical agent is abacteria type that digests the VES directly.
 36. The fluid of claim 33where the biochemical agent is selected from the group consisting ofbacteria, fungi, and mixtures thereof, that have been bio-technicallyengineered by a technique selected from the group consisting of growthchallenge, culture for selective gene expression, genetic modificationthrough gene splicing techniques, and combinations thereof.
 37. Thefluid of claim 33 where the biochemical agent is selected from the groupconsisting of bacteria and fungi that digests a component of the fluidother than the VES to produce a by-product that in turn degrades the VESsurfactant.
 38. The fluid of claim 33 where the component is selectedfrom the group consisting of alcohols, monoalcohol polymers, alcoholfatty acids, alkyl fatty acids, glycols, starches, potassium formate orother formate, polysaccharides, sugars, sugar chelants, sugar alcohols,aliphatic alcohols, reservoir crude oils, proteins, VES stabilizers,amino acids, acetates, phosphonates, phospholipids, lactates,isocyanates, esters, turpenes, butyrates, propionates, salicylates,hexaonates, nitrilotriacetic acid, ethylenediaminetetra-acetic acid,amino chelant compounds, polyaspartates, pyrrolidone compounds, andmixtures thereof.
 39. The fluid of claim 37 where the by-product is anenzyme selected from the group of enzymes that (a) catalyze a reactionto break down the VES directly, and (b) catalyze a reaction utilizinganother component of the fluid other than VES to produce a by-productthat in turn degrades the VES surfactant.
 40. The fluid of claim 39where the enzyme is lipase.
 41. The fluid of claim 33 where the VES isselected from the group consisting of amines, amine salts, quaternaryammonium salts, amidoamine oxides and amine oxides.
 42. The fluid ofclaim 33 where the VES is tallow amido propylamine oxide (TAPAO). 43.The fluid of claim 33 where the VES is erucyl bis-(2-hydroxyethyl)methylammonium chloride.
 44. The fluid of claim 33 where the biochemical agentis bacteria selected from the group consisting of the classesEnterobacter, Enterococcus, Pseudomonas, Bacillus, Leptospirillum,Clostridium, Arthrobacter, Rhodobacter, Rhodococcus, Micrococcus,Serratia, Thermoanaerobacter, Thiobacillus, Pyrococcus, Lactobacillus,Achromobacter, Propionibacterium, Thermomicrobium, Nitrobacter,Nitrosomonas, Sulfolobus, Methanobacterium, Methanococcus, Bacteroides,Fusobacterium, Syntrophus, Acetogenium, Actinomyces, Acetobacter,Citrobacter, Alteromonas, Acinetobacter, Flavobacterium,Corynebacterium, and mixtures thereof.
 45. The fluid of claim 33 wherethe biochemical agent is bacteria selected from the group consisting ofArthrobacter globiformis, Enterobacter colacae, Lactobacillussporogenes, Lactobacillus bulgaricus, Lactobacillus acidophillus,Pseudomonas fluorescens, Pseudomonas aeruginosa, Actinomyces israeli,Pseudomonas putida, Nitrobacter vulgaris, Arthrobactor M153B, Bacillusmegaterium, Thiobacillus novellus, Bacillus subtilis, Bacilluslicheniformis, Clostridium pasteurianum, Corynebacteriumglucuronolyticum, Enterococcus faecalis Pyrococcus abyssi, RhodococcusST-5, Rhodococcus 33, Rhodococcus H13-A, Thermoanaerobacter ethanolicus,Thermoanaerobacter mathranii, Nitrosomonas europaea, Propionibacteriumpropionicus, Rhodobacter sphaeriodes, Clostridium thermocellum,Clostridium ATCC #53797, Clostridium ATCC #53793, Corynebacteriumhydrocarbolastus, Acetomicrobium flavidum, Acetobacter pasteurianus,Serratia marcescens, Acetobacter aceti, Achromobacter xylosoxidans, andmixtures thereof.
 46. The fluid of claim 33 where the microbe metabolicactivity of the biochemical agent can be enhanced by a parameterselected from the group consisting of temperature, pressure, pHadjustment of the fluid to between about 2.0 and 11.0, and combinationsthereof.
 47. The fluid of claim 33 where the amount of biochemical agentranges from about 0.01 to about 20.0 percent by volume based on thetotal volume of fluid.
 48. An aqueous fluid comprising water; at leastone viscoelastic surfactant (VES), in an amount effective to increasethe viscosity of the aqueous fluid; and bacteria, in an amount effectiveto reduce the viscosity of the gelled aqueous fluid after the viscosityof the aqueous fluid has been increased, where the bacteria reduces theviscosity of the gelled aqueous fluid by disaggregating or rearranging amicelle structure of the VES.
 49. The fluid of claim 48 where the VES isselected from the group consisting of amines, amine salts, quaternaryammonium salts, and amine oxides.
 50. The fluid of claim 48 where theVES is tallow amido propylamine oxide (TAPAO).
 51. The fluid of claim 48where the bacteria is selected from the group consisting of Arthrobacterglobiformis, Enterobacter colacae, Lactobacillus sporogenes,Lactobacillus bulgaricus, Lactobacillus acidophillus, Pseudomonasfluorescens, Pseudomonas aeruginosa, Actinomyces israeli, Pseudomonasputida, Nitrobacter vulgaris, Arthrobactor M153B, Bacillus megaterium,Thiobacillus novellus, Bacillus subtilis, Bacillus licheniformis,Clostridium pasteurianum, Corynebacterium glucuronolyticum, Enterococcusfaecalis, Pyrococcus abyssi, Rhodococcus ST-5, Rhodococcus 33,Rhodococcus H13A, Thermoanaerobacter ethanolicus, Thermoanaerobactermathranii, Nitrosomonas europaea, Propionibacterium propionicus,Rhodobacter sphaeriodes, Clostridium thermocellum, Clostridium ATCC#53797, Clostridium ATCC #53793, Corynebacterium hydrocarbolastus,Acetomicrobium flavidum, Acetobacter pasteurianus, Serratia marcescens,Acetobacter aceti, Achromobacter xylosoxidans, and mixtures thereof. 52.The fluid of claim 48 where the bacteria has been bio-technicallyengineered by a technique selected from the group consisting of growthchallenge, culture for selective gene expression, genetic modificationthrough gene splicing techniques, and combinations thereof.
 53. Thefluid of claim 48 where the bacteria is a type that attacks the VESdirectly.
 54. The fluid of claim 48 where the amount of bacteria presentranges from about 0.01 to about 20.0 percent by volume based on thetotal volume of fluid.
 55. The fluid of claim 48 where the microbemetabolic activity of the bacteria can be enhanced by a parameterselected from the group consisting of temperature, pressure, pHadjustment of the fluid to between about 2.0 and 11.0, and combinationsthereof.